All images were snagged, with some thought and care, and even with some credit, from Google Images.
Digression One: The Milky Way Galaxy, and its closest neighbor in our local group, the Andromeda Galaxy, will only be mentioned here and there in this the last of my little essays because they are both examples of a Normal Galaxy, which is one where:
1) its total energy output equals the total emissions of all its stars and
2) its centrally located supermassive black hole has very little gas for capture and so, hasn’t, and probably won’t, form a Quasar or a Blazer at its center and as cool as a normal galaxy is, it is nonetheless a subject best left for another time.
First Photo: from www.universetoday.com, The Milky Way
Second Photo: www.nasa.gov The Andromeda Galaxy
On-the-other-hand, an Active Galaxy is one in which
1) its total energy output far exceeds the total emissions of its stars with the most energetic of these galaxies being able to emit hundreds or even thousands of times more energy per second than the Milky Way (and seriously, how cool is that!) and
2) its centrally located supermassive Black Hole has more than enough gas to capture so that it can form the active galactic nuclei (AGN) of a Blazar/ Quasar.
Black Holes (briefly…very briefly)
Even though the term was first used in 1967, the idea of black holes has been imagined for centuries and was most famously predicted by Einstein’s General Relativity.
When very massive stars die, their outer gases explode to a supernova while their inner core implode with such density that the fabric of spacetime can no longer support them (imagine a star with ten Solar masses squeezed into a sphere about the diameter of New York City). They appear to come in two distinct types: Stellar and Supermassive.
The basic formation process of black holes is understood. If a black hole passes through a cloud of interstellar matter, it will draw that matter inward in a process known as accretion, forming an accretion disk around itself. A similar process also happens when a normal star passes close to a black hole causing it to tear apart as the black hole draws the star inward toward itself. As the attracted matter accelerates and heats up, it emits x-rays that radiate into space.
First Graphic: from en.wikipedia.org, Artist's rendition of a black hole with an orbiting companion star that exceeds its Roche limit*. Mass from the companion star is drawn towards the black hole, forming an accretion disk.
* The minimum distance in which a large satellite can approach its primary body without being torn apart by tidal forces.
They are called ‘black holes’ not because they are holes themselves or because of their distortion of spacetime, but because they are stars so dense, their gravity so strong, that light cannot escape from their surface so, they cannot be seen.
Digression Two: Allow me to try and put this ‘black hole’ thing into perspective. When it is said that light cannot escape a black hole’s surface, what is being talked about is the escape velocity of an object from another object’s gravity.
For instance, the escape velocity of a rocket from Earth’s gravity is 7 miles per second, meaning that a rocket must travel at a velocity of at least 7mi/sec to be able to pull away from earth’s gravity before then carrying on into interstellar space. Anything less and a rocket will plummet back to Earth’s surface.
For a black hole, its escape velocity exceeds the speed at which light travels or 186,000 miles per second so when light tries to escape, it is pulled back to the black hole’s surface just like a rocket is pulled back to Earth’s surface (Okay, seriously, that just freakin’ blows me away). And so, since nothing exceeds the speed of light, nothing can escape from a black hole. And so, at a black hole, it would seem that gravity is King!! And most likely a whole new physics is needed. One where the speed of light can be exceeded?? (Could happen!!)
Stellar Black Holes:
These are detected only when another star comes close enough for some of the matter surrounding the star to be caught up by the black hole's gravity, sending out x-rays in the process. However, since stellar black holes lead isolated lives, most of them are impossible to detect, although it can be estimated from the number of stars large enough to produce such black holes, that there are as many as ten million to a billion roaming the Milky Way alone.
Supermassive Black Holes
These are millions, possibly even billions, of solar masses in size and live out their lives at the center of most, if not all, galaxies including the Milky Way. Like stellar black holes, they are detected by watching for their effects on nearby stars and gas.
Both Graphics: a black hole as ‘seen’ moving through space with its lensing effect and with the rainbow funnel showing a black hole’s distortion of spacetime.
Blazars and Quasars
To make things easier, please note that the same basic object -- a supermassive black hole with a surrounding accretion disk, which produces a jet -- is called a blazer if it’s viewed with the jet directed toward Earth’s line of sight and is called a quasar if it’s viewed with the jets running more parallel to the Earth’s line of sight.’ Quasar’ will be used throughout (and even if blazer is a very cool word…very 1950s).
Graphic: http://www.astronomy.com/ pretty much says it all
First discovered in 1963, scientists have very little real understanding of what a quasar (a quasi-stellar radio source or quasi-stellar objects QSOs) is, but believe that since they lie at its outer edges, they are the most distant objects yet detected in the Universe. Their energy takes billions of lightyears to reach the Earth and for this reason the study of quasars can provide much information about the early stages of the Universe.
For instance, since very little is known about the evolutionary process of galaxies, it is possible that quasars, as old as they are, may represent a very early stage in the formation of young and very active galaxies.
Thousands have been identified, including a kind of quasar that doesn’t emit any radio waves. These "radio quiet" quasars are now thought to comprise about 99 percent of all quasars.
First Photo: from www.windows2universe.org; Quasar Host Galaxies, Hubble Space Telescope image of STScI
Second Photo: from haysvillelibrary.wordpress.com, Colliding galaxies that can give birth to Quasars. (think us and Andromeda in several billion years!!!)
First proposed by the Russian scientist, Yakov Zeldovich, most astronomers believe that a quasar represents an extreme case where large quantities of gas, forming its accretion disk, pour into a supermassive black hole so rapidly that the energy output is a thousand times greater than that of the galaxy itself. As the accretion disk spins ever faster inward, the friction between all of its particles gives off enormous amounts of light, along with other forms of radiation such as x-rays thereby drowning out, because of its brightest, all the light of all the other stars in that galaxy.
During the lifetime of an active galactic nuclei or AGN, the black hole and its accretion disk will undergo a quasar phase where intense radiation is blasted from the superheated gases surrounding the black hole.
First: A photograph taken by Chandra, NGC 4151, or as it’s been dubbed ‘The Eye of Sauron’, is a spiral galaxy with an actively growing supermassive black hole at its center.
Second: A graphic showing the wind from accretion disk around a black hole.
However, not all the matter in the gravitational whirlpool will fall into the black hole. In many quasars, part of the gas escapes as a hot wind that is blown away from the accretion disk at speeds as high as a 1/10th of the speed of light.
Even more dramatically, as the black hole crushes out of existence an amount of matter equal to the mass of the Sun in just one year, enormous amounts of energy are ejected along the black hole's north and south poles. Referred to as cosmic jets, these are the high-energy jets that radio and X-ray observations show exploding away from some supermassive black holes. These jets move at nearly the speed of light in tight beams that blast out of the galaxy and travel hundreds of thousands of lightyears.
Second: from www.universetoday.com (I quote directly)
Hubble Space Telescope Images of M87. At right, a large scale image taken with the Wide-Field/Planetary Camera-2 from 1998. The zoom-in images on the left are of the central portion of M87. HST-1 is a knot in the jet from the SMBH
(NASA and the Hubble Heritage Team (STScI/AURA), J. A. Biretta, W. B. Sparks, F. D. Macchetto, E. S. Perlman)
And actually, some scientists even believe that quasars may be distant points in space where new matter may be entering this Universe, thereby making a quasar the opposite of a black hole, but this is only speculation. Undoubtedly, it will be awhile before it is really understand what these strange objects are.
Finding answers for many of the important quasar questions was a major reason for the push for a space telescope in 1978, which ultimately resulted in the Hubble Space Telescope. (YAY!! YAY!! YAY!! and so on) Spectacular images have shown that quasars do in fact form in galaxies, but the images have also revealed other surprising information:
For instance, quasars live in a variety of galaxies, some actually quite normal and some colliding with their neighbors. So, although Hubble has yielded more clues, many questions still remain about these strange objects.
What Has Been Learned
1. Quasars give off enormous amounts of energy
2. Quasars can be a trillion times brighter than the Sun
3. Quasars radiate as much energy per second as a thousand or more galaxies and (my personal favorite little observation)
4. Quote: ’ it is as if a powerhouse the size of a small flashlight produced as much light as all the houses and businesses in the entire L.A. basin!’
5. All of this activity is from a region that has a diameter of about one millionth that of its host galaxy, but which is still, in most cases, larger than our Solar system.
6. Quasars are intense sources of visible light but also of X-rays and are actually the most powerful type of X-ray source yet found. They also emit ultraviolet rays, infrared waves and gamma-rays. Some quasars are so bright they can be seen at a distance of 12 billion lightyears with the most distant, ULAS J1120+0641, at about a distant of 13 billion lightyears.
Note: A lightyear is the distance light can travel in one year or about 7 trillion miles so if the Universe can be taken to be about 13.7 billion years old, and the light from the Quasar, ULAS J1120+0641, has taken 13 billion lightyears to arrive here then, when we see it, we are looking back to a time only 0.7 billion (700 million) years after the Universe’s birth. (whoa!)
7. Quasars also have the largest red shift of any other objects in the Universe, which is determined when the speed and distance of far away objects is determined by measuring its light spectrum. If the colors of its spectrum are shifted toward the red, the object is moving away from Earth, toward the blue, the object is moving toward Earth. The greater the redshift, the farther away the object and the faster it is moving.
8. Since quasars do have such a very high redshift, they are extremely far away and are moving away from Earth at extremely high speeds. It is believed that some quasars may be moving away from Earth at 150,000 miles (or 240,000 kilometers) per second or nearly 8/10th the speed of light.
Graphic: 'Shows' how, if an object is moving away from us, its lightwave becomes longer (decrease in frequency) or redshiftes and how its lightwave becomes shorter (increase in frequency) or blueshiftes if an object is moving toward us.
Note: Almost all objects in the Universe are redshifted with a few exceptions. Andromeda, the largest galaxy in the Milky Way’s local group, is blueshifted as are nearby stars such as Bonard’s Star. Since the Andromeda Galaxy is blue-shifted that means it’s moving toward us and so, in some far off and distant time (well after the Sun has gone red giant) it is believed that the Milky Way and Andromeda galaxies will go bump in the night, colliding in a kind of dance of death that will eventually combine them into one much larger galaxy.
And so, to quote one source (I forget where…sorry)
‘Quasars have been so elusive and mysterious that the hunt to define them would have taxed even the superior analytical skills of detective Sherlock Holmes’ (way to tie-in, am I right?)
I don’t know about how right I am, but I certainly am nearly done. With each of these three little essays, I started out thinking I was researching one thing and, as I learned, I quickly, or sometimes not so quickly, realized I was actually researching something quite different. The way of life and just as it should be.
#58_Stars & the Nebulae Where They Are Born
#60_The Standard Model_The Twelve Fundamental Matter Particles and Three of the Four Fundamental Force Carrying Particles